Various methods exist for rehabilitating damaged pipe lines and other conduits. These methods range from physically removing the damaged section of the pipe or conduit and replacing it with a new section, to providing a reinforced lining for the pipe or conduit.
Reinforced linings are typically formed from composite materials and are impregnated on site, or pre-impregnated at a remote location, with a curable resin system. When the resin system cures, it hardens and forms a protective shell in the pipe or conduit.
There are generally two types of resins systems which may be used in such linings, ambient cure systems and heat activated systems. Ambient cure systems can experience many problems in pipe rehabilitation. For example, if the temperature is too cold, which may occur in underground sewer pipes, the resin will not cure and the lining will collapse unless it retains some internal support structure. Conversely, on warm days, the system may begin to cure before the lining is properly placed in the pipe. Accordingly, high temperature activated resin systems are preferred.
High temperature resin systems require a heating element to activate the resin system once the lining is in place in the pipe or conduit. In the past, heated water, steam or gas was circulated in the lining to cure the resin. These operations required expensive equipment, and typically took a long period of time to ensure a proper cure.
Another method of heating a composite lining was to place a heating element directly into the composite material. The heating element could take the form of a conductive element, such as a layer of conductive fibers in the lining. The lining was positioned in the pipe or conduit and then inflated to press against the walls of the pipe or conduit. An electric power source connected at both ends of the lining would cause an electric current to flow from one end of the lining to the other end to resistively heat the conductive layer to cure the resin. Graphite fabric was sometimes used as the conductive layer.
Such systems were able to obtain the benefits of having the current run lengthwise through the lining, but required providing electrical connections at both ends of the lining. Depending on the structure and location of the pipe being rehabilitated, it is sometimes difficult or impossible to place a cable at the far end of the lining to complete the electrical circuit. Additionally, even if possible to place the cable at the far end of the lining, it may require an extremely long cable to do so which is undesirable. Finally, when access to the far end of the lining is through a manhole located on a street, it may become necessary to close the street to effect the repair.
U.S. Pat. No. 4,768,562 (Strand) discloses another method of rehabilitating a pipe with a lining having an integral heating element. Strand discloses pulling an elastomeric tube through a damaged pipe. The elastomeric tube has a diameter substantially equal to the inner diameter of the pipe and is encompassed by an electrically conductive resinated fiber lattice that radially contracts when axially elongated. The elastomeric tube and resinated fiber lattice are axially tensioned, whereby the maximum diameter of the liner is elastically reduced by the resultant elongation thereof. The resin is then partially polymerized so that the liner is maintained in such condition. After being pulled through the pipe, an electric current is directed through the resinated fiber lattice, thus softening the resin by electrical resistance heating. The elastomeric tube, no longer restrained by the resinated fibre lattice, resiliently expands radially outwardly until it resumes its prior shape. The liner is further heated electronically so as to completely polymerize the resin, thereby bonding the liner to the inner wall of the damaged pipe.
U.S. Pat. No. 5,010,440 (Endo), discloses another method of rehabilitating a pipe with a lining having an integral heating element. Endo discloses a lining constructed having a tubular conductive layer. Copper wires are affixed lengthwise on the lining by means of strips of insulating tape which are coated with an adhesive material on one side. The copper wires are affixed along the edges of the lining before it is formed into a tubular shape as shown in FIG. 2(a) of Endo. Although the edges of the lining are brought into contact with each other, they are electrically insulated from each other by means of the insulating tape. This places the copper wires physically close to each other in the lining. The copper wires are used to cause an electric current to flow circumferentially through the lining.
Contrary to the approach taken by Endo, the methods of the present claims cause a current to flow lengthwise through the lining as opposed to circumferentially. A more thorough and faster cure is affected by causing the current to run lengthwise through the lining.
Further, the present methods reduce or eliminate potential problems faced by Endo. For instance, ripping or tearing of the insulating tape during placement of the Endo lining in a pipe may result in a short circuit, which may interfere with proper heating and curing of the resin. Additionally, the Endo linings may require a large current, and such large currents may themselves create problems. These problems are not encountered utilizing the methods of the present invention.